1. Field of the Invention
The present invention relates to a sheet stacking apparatus capable of stacking sheets on a sheet stacking portion, a control method of the sheet stacking apparatus, and a storage medium.
2. Description of the Related Art
Conventionally, there has been provided a sheet stacking apparatus for discharging sheets to a sheet stacking portion that can be lifted and lowered.
The above sheet stacking apparatus discharges the sheets on which images are printed to a sheet stacking portion from a sheet discharge port after the images are printed on the sheets. The sheet stacking portion is lowered every time the sheet is discharged to the sheet stacking portion in such a manner that an uppermost surface of the sheets stacked on the sheet stacking portion is positioned in a vicinity of the sheet discharge port, and thus the sheets discharged from the sheet discharge port can be stably stacked thereon.
In a case where an obstacle which interrupts the lowering of the sheet stacking portion is placed under the sheet stacking portion, the sheet stacking portion may collide with the obstacle in the course of lowering the sheet stacking portion. If the sheet stacking portion is forced to lower after colliding with the obstacle, a load is applied to a driving unit for lowering the sheet stacking portion, and thus the sheet stacking portion or the driving unit may be damaged.
Japanese Patent Application Laid-Open No. 2001-226022 discusses a technique for displaying a warning message for prompting a user to remove an obstacle while stopping sheet discharge and lowering of the sheet stacking portion when lowering of the sheet stacking portion is interrupted by the obstacle.
In the above conventional technique, stacking sheets without removing the obstacle is not taken into consideration.
A space under the sheet stacking portion is easily accessible by the user because the space is close to the apparatus. Therefore, for example, the user may place bundles of sheets under the sheet stacking portion so that the user can promptly supply a bundle of sheets when there is a shortage of sheets in the apparatus. Further, the user may place a recording agent such as toner or ink under the sheet stacking portion so that the user can promptly supply the recording agent when there is a shortage of the recording agent in the apparatus. Furthermore, the user may place an instruction manual under the sheet stacking portion so that the user can promptly refer to an operation method of the apparatus.
There may be a case where the user would like to stack sheets while intentionally placing these items under the sheet stacking portion.
The user can complete sheet stacking without removing the obstacle in a case where the user stacks a small number of sheets.
On the other hand, if the user stacks a large number of sheets, it is better for the user to stack sheets after removing the obstacle. This is because by removing the obstacle, the user can reduce a possibility of suspending the sheet stacking operation.
However, with the conventional technique, it is difficult for the user to easily determine how many sheets can be stacked after removing or without removing the obstacle.
Therefore, it is difficult for the user to easily determine whether the user should stack sheets after removing or without removing the obstacle.